1. Technical Field
The present invention relates to axial flow compressors and in one aspect relates to a method and apparatus for mounting the stator blades in axial flow compressors wherein resilient spacers are used between at least some of the stator blades to compensate for wear and maintain the stability of the stator blades during extended operation of the compressor.
2. Background
Axial flow compressors are well known and are commonly used in many commercial operations. For example, in operations involving gas turbines (i.e. the generation of electricity), axial flow compressors are typically used to supply the compressed air necessary to support the combustion needed for driving the turbine. While the details between particular axial flow compressors may vary, generically, an xe2x80x9caxial flow compressorxe2x80x9d is a compressor which is basically comprised of a rotor axially mounted inside of a stator casing. Both the rotor and stator casing include rows of blades which rotate with respect to each other to compress the gas as the gas flows through the compressor.
Typically, the stator of an axial flow compressor is comprised of rows of stationary blades that are attached to the compressor casing within which a rotor is coaxially mounted. The inner surface of the casing has a plurality of circumferential grooves (e.g. up to 17 or more) formed therein which are axially spaced from each other along the casing. A plurality of individual stator blades are positioned, side by side, into each groove and are radially spaced around the groove in a manner which will provide the best aerodynamic effect as a gas flows therethrough. That is, desirably the stator blades will be equally spaced from each other about the inner circumference of the casing, i.e. the blades will be equally spaced within the 360xc2x0 of each stage of compression.
Ideally, each individual stator blade would be identical in size and shape to all of the other blades so that the mounting base of each blade would firmly abut the bases of the blades on either side thereof when all of the blades were positioned within a particular groove in the casing. This physical contact between adjacent blades would insure that the blades were all equally spaced and would firmly fix the blades in position so that none of the blades could move within the groove once they were in position.
However, in the real world, due to the relatively large number of blades that may be required in each row (e.g. up to 80 or more blades) and due to the tolerances involved in standard manufacturing processes, a certain amount of xe2x80x9cslopxe2x80x9d is almost sure to remain when all of the stator blades are loaded into a particular groove. That is, there is always a very small, unfilled space remaining within the groove after all stator blades have been positioned which, if not compensated for, will allow slight movement between certain stator blades within the grooves which, in turn, can cause severe problems during operation of the compressor.
To compensate for this remaining space in known axial flow compressor, manufacturers of these compressors normally provide flat spacers, i.e. xe2x80x9cshimsxe2x80x9d, of different thicknesses to specially match the profile of the particular groove in which the stator blades are positioned. As will be understood in the art, these individual shims are positioned between selected stator blades as needed to provide equal spacing of the blades and fix the blades in position. Normally, only a relatively few shims will be needed since the majority of the mounting bases of adjacent blades will be in abutment with each other.
While these flat shims function well in properly spacing the stator blades and holding them in a fixed relationship to each other, the shims undergo continuously micro-motion and other detrimental forces during operation of the compressor which can result in severe wear on the shims. That is, the profiled tabs, which hold the flat shim in the groove within the casing, can break or be eroded away whereupon the broken shim can xe2x80x9cwigglexe2x80x9d out from between the stator blades and into the interior of the compressor casing. As will be recognized, such a loose piece of metal (i.e. a loose shim) can do serious damage to both the stator and the rotating rotor blades. Further, once the broken shim no longer fills the space between adjacent stator blades, those blades are now free to start vibrating, which can quickly lead to a catastrophic failure of the compressor.
The present invention provides a axial flow compressor and a method and apparatus for mounting the stator blades in the compressor whereby the micro-motion and other detrimental forces on the spacers (e.g. shims) between the stator blades are alleviated.
More specifically, the axial flow compressor of the present invention is comprised of a stator casing having a rotor axially positioned therein. The casing has at least one internal circumferential groove into which a plurality of individual stator blades are positioned. Typically, the casing will have a plurality of axially-spaced grooves (e.g. up to 17 or more) with each groove effectively representing a stage of compression. As with prior art compressors of this type, due to the large number of stator blades (e.g. up to 80 or more) and the machine tolerances involved, there is usually a small space remaining within the groove after all of the stator blades have been positioned therein.
The blades are then readjusted until substantially the same distance exists between each of the blades. It should be recognized that there will not necessarily be a space between every two blades but more likely, there will only spaces between a relatively few blades. In accordance with the present invention, a resilient spacer is positioned within each space so that all of the blades are substantially equally positioned and are firmly held against movement within the groove.
Preferably, each resilient spacer is formed in the shape of a leaf spring which is basically a resilient, curved plate comprised of a corrosion-resistant, hardened material (e.g. stainless steel). The curved plate has a tab at each side thereof which, in turn, is adapted to fit into the internal circumferential groove on the casing to hold the spacer in the groove. The overall thickness of the curved plate, which may vary (e.g. {fraction (1/16)}xe2x80x3 to {fraction (3/32)}xe2x80x3 or the like), when in a relaxed state is substantially equal to the space between two adjacent stator blades into which the curved plate is to be positioned.
The resilient spacers of the present invention not only spaces and prevents movement of the blades within the groove but they also provide a resilient force respective two adjacent stator blades whereby the aerodynamic loads, present during operation of compressor, will compress/relax the resilient spacers thereby virtually eliminating the micro-motion and inter-fretting of the shims previously encountered by the flat shims typically used in prior art axial flow compressors.